1. Field of the Invention
This invention relates generally to a tool for cleaning the internal surfaces of a control rod drive mechanism which may be used in a nuclear reactor vessel.
2. Description of Related Art
A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends, e.g., by a bottom head and a removable top head.
At various times during the operational life of a nuclear reactor, there is a need to remove the core and internals from the reactor vessel for maintenance. For example, graphite seals in the control rod drive mechanism (CRDM) wear out gradually, and corrosion products build up inside the drive, which must be cleaned to reduce contamination levels and maintain performance. If regular maintenance of the CRDM is not performed, excessive seal leakage may lead to operational difficulties or inoperative CRDMs.
CRDMs reside in the bottom of the core, and are a natural collection point for any crud or debris that is released from the core. The process of scramming the CRDM generates mechanical, thermal and hydraulic shocks in the vessel, while simultaneously direct high volumes of water through the CRDM to create the desired control rod insertion. This can result in very high levels of contamination and radiation on the surfaces of the CRDM.
Accordingly, a need exists for cleaning the control rod drive mechanism to minimize dose and contamination to the workers performing the CRDM maintenance, as well any other personnel who may be in the area where the drive is stored, handled or installed.